Field
The described technology generally relates to a device and a method for an electrolytic coating of an object, for example, a wire.
Description of the Related Technology
It is well known to coat metallic objects, such as wires electrolytically in an electroplating plant, for example, by tin coating. For this, the wire and the coating material are immersed into an electrolyte bath, and therefore, they are electrically conductive connected to each other. If the wire and the coating material are connected to different poles of a DC power source, then—in the case of a sufficiently high voltage—an electric current flows, which causes the ions in the electrolyte to migrate to the wire or to the coating material, respectively (electrolysis).
The wire is connected to the negative pole of the DC power source and forms the cathode. The positively charged metal ions migrate in the electrolyte to the cathode and then they receive the electrons (electrochemical reduction), whereby metal atoms are formed, which attach to the wire to be coated. Concerning the anodes, a distinction is made between the so-called soluble anodes and the so-called insoluble anodes. For the soluble anodes, the anode metal dissolves by donating electrons to the circuit (electrochemical oxidation) and it goes as a metal ion into the electrolyte (usually a salt solution). However, the insoluble anodes do not dissolve, but serve only for contacting the electrolyte to form the metal ions in the electrolyte (usually a metal salt solution). In the case of the soluble anodes, these anodes dissolve with time; in the case of the insoluble anodes, the electrolyte is depleted of the metal with time.
For the acid electrolytes, such as tin electrolytes on the basis of methane sulfonic acid, for the use of soluble anodes, there is always a difference between anodic and cathodic current efficiency. The anodic current efficiency is usually close to 100%, while the cathodic current efficiency, for example for the methane sulfonic acid tin electrolytes, is usually somewhere between 95% and 97%. The cathodic current efficiency depends in particular on the coating material, the electrolyte and the operating parameters (bath temperature, agitation, current density, etc.).
For conventional electroplating systems, the above described difference between the anodic and cathodic current efficiency results in an increase of the metal concentration in the electrolyte which has to be corrected upon reaching a predetermined upper threshold value. To keep the metal concentration in the electrolyte within a predetermined range, the electrolyte can be regenerated, for example, regularly or continuously.
On the other hand, for using the insoluble anodes, it is required to correct the metal concentration upon reaching a predetermined lower threshold value. To keep the metal concentration in the electrolyte within a predetermined range, it is also possible in this case to regenerate the electrolyte periodically or continuously. For example, DE 195 39 865 A1 discloses a throughput electroplating plant with insoluble anodes in the electrolytic cell, wherein the electrolyte is enriched in a regenerating room continuously with metal ions.
Furthermore, DE 195 39 865 A1 describes the use of the insoluble anodes in the electrolytic cell, which are shielded from the electrolyte by diaphragms, and the use of the soluble anodes in an external regenerating room for supplementing the metal content in the electrolyte.